Zeng et al. (2005) have argued that band limiting and compressing the FM variations to “slow” variations may be beneficial for the hearing impaired. U.S. Pat. No. 7,225,027 dealing with cochlear implants (CI) describes a signal processing strategy termed FAME (Frequency-Amplitude-Modulation-Encoding). The difference between current CI frequency encoding strategies and the FAME strategy is that previously only a fundamental frequency has been used to modulate the carrier across some or all bands in the fundamental frequency encoding strategies, while in the applications of FAME strategy in accordance to their invention, the band-specific frequency modulations (which may or may not carry fundamental frequency information) will be extracted and used to modulate the carrier frequency in the corresponding band.
In summary, the current state of art suggests that correlated FM and AM signals are produced in natural speech (c.f. Zhou, Hansen and Kaiser (2001)), and that the FM signals are important for negative signal to noise ratios for normal hearing persons, but the FM extraction may be impaired among people with cochlear impairment (c.f. Swaminathan and Heinz (2008)). However, hearing impaired can utilize the AM cues. In addition, there are inventions made for CI where the signal is made available to the CI-user by extracting FM information and presenting these by a frequency modulation carrier within a given (narrow) band.